It's time (actually, overdue), to have the transmission fluids changed in my P-30/454. (No problems - I just don't want any...)Obviously I'd like to end up with the cleanest possible condition after dropping the pan, screen cleaning/changing and a power flush of the torque converter.....

It seems to be that regardless of sequence (pan drop - then power flush, or vice versa), I'll end up with some old fluid somewhere in the system.....

Power flushing first, then dropping the pan means new fluid lost, but I guess it minimizes contamination....

I'm I thinking straight here?....Or am I getting concerned about something petty?

In an ideal world, we'd all dismantle our transmissions, clean every part individually, mike everything up, change out anything that wasn't up to specs, then reassemble & refill . That, of course, would be overkill. The question is how far do you go before it becomes overkill.

IMHO - Unless your present fluid is discolored, dirty, and smells burnt (in which case you need more than a change of fluiid) if you drop the pan, drain, flush the converter, let it drip until you can't stand to wait any longer, then refill, you've done more than the standard oil change. (Does the TH 400 have a replaceable filter? If so, of course change that too.)

The key to transmission life is keeping it cool. In a motorhome, in the best of circumstances, you'll see some high temperatures, especially on hills, and if you pull a toad. Follow the mfrs. specs, but be more concerned about the condition of the fluid, than the length of service.

The TH400 has a replacable filter.

You can power flush yourself with the tranny's own pump by catching fluid from the cooler through a clear vinyl tube slipped over the steel tubing before it enters the transmission. Idle the engine. Have a helper stop the engine and add a quart of new fluid every time a quart of old fluid pumps out.

Whoa Bill....Hang on here...You're scaring me!....Last time I tried something like that with my lawn tractor's hydrostatic transmission, I was afraid that the EPA was going to show up and declare my driveway a Superfund Clean-Up site.........

But let's say I do make this a D-I-Y project, (Geeze, I just HATE it when I start thinking this way... ), how much new fluid would you say I need to get it to run clean - twice capacity?, more-less? And do I need to shift through the gears to maximize drainage? Inquiring minds want to know....

quote:

Originally posted by Lee:
Whoa Bill....Hang on here...You're scaring me!....Last time I tried something like that with my lawn tractor's hydrostatic transmission, I was afraid that the EPA was going to show up and declare my driveway a Superfund Clean-Up site.........

But let's say I do make this a D-I-Y project, (Geeze, I just HATE it when I start thinking this way... ), how much new fluid would you say I need to get it to run clean - twice capacity?, more-less? And do I need to shift through the gears to maximize drainage? Inquiring minds want to know....

It will be two or three qts more than full capacity, including converter. Maybe 14 qts. Consider Synthetic. Synthetic fluid runs cooler and has a higher flash point. Many gas engine fires are the result of overheated trans fluid coming up the fill tube and spilling onto the exhaust. I posted the whole flushing rain dance here before, but am unable to find it by this site's search function. It seldom is much good at finding my old posts.

Here goes:

There are two lines on the trans. Run until one is noticeably hotter. That is the “out” line. The cooler one is the “in” line. Commit this to memory or write it down. (I have done neither)

Drop the pan and install a B&M drain plug (sold by Summit). Smell the fluid. If it smells burnt, close it up, refill and start saving. The drain plug fitting allows a trans temp gage sender to be used as a drain plug. Replace pan and filter. .Top off with new fluid.

Disconnect the “in” line and slip a snug-fitting length of clear vinyl tubing over it. I seem to remember dipping a 3/8 line in hot water to get a good fit. Cut a short length of the vinyl tubing, plug or melt one end shut and fill it with new fluid. Attach the filled short length to a vertical section of the clear line. Stay with me here.....It will be used for color comparison.

Chock wheels and set handbrake.

Have your assistant fire up the engine, and run it through the gears at idle, holding one foot on the brake whenever the engine is running. Have him/her shut off when you see one quart is pumped out. I use a translucent container with marked graduations. Have him/her replenish the quart lost and do it again until the fluid coming out matches the new sample you attached to the out hose. Go ahead and waste another quart just to be sure.

Check level with dipstick.

An easier, but not cheaper way is to take it and your own fluid to a shop with a TransTech II machine and have them put in your fluid. http://www.bedfordindustries.com/mtt1100.htm They might want a lot of money for a motor home, though. And some shops are a little difficult about folks who bring in their own fluids. Many shops do not drop the pan and change the filter, though, or charge extra for it.

I use Castrol Syntec synthetic ATF fluid in my TH400. Art Carr recommends it. (the REAL Art CArr, not the ones who use his name now) Allison extends their trans warranty by lots of miles if you use another of Castrol's tranny fluids, Transynd. Per the Allison Service Tip #1099B, if you have the new Allison 6 speed and change to Transynd now, and Transynd again at 37,000 miles, you are then good for 150,000 miles. That doesn’t apply to Syntec, or your TH400 specifically, but it gives you an idea of what their engineers think of Transynd in particular and synthetic ATF in general. Transynd is approved as a replacement for Dexron III.
Syntec ATF is listed as replacement for Both Dexron III and Mercon.

I have also used Red Line hi temp synthetic ATF, and been happy with it. Their Hi Temp synthetic ATF is listed as a replacement for Dexron III and Mercon. Summit sells it. http://www.redlineoil.com/products_gearlubricants.asp?p...rodID=59&subcatID=19
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